Beneficial Nematodes, Invisible Helpers Balance Soil Biology

It is fun to talk about the garden in terms of battles. But honestly we need to get out of this mindset. It is this very mindset that brought horticulture and agriculture to such an unhealthy place. In general, our attempts at controlling pests is misguided thinking. Those very attempts led to us creating and using products that should never have been employed. Once you start thinking as part of the biology of your sphere as an enemy, and attack that enemy using methods with so much collateral damage, you begin to tear apart your own biology.

Basic diagram of soil microbiology. Click to enlarge.

For me, my goal in horticulture is learning to continue enjoying plants the way I do, but also learning to feed and care for the biology of my own sphere. Most organisms that we consider a pest and harmful to people and plants are opportunistic organisms that attack a disturbed system. In a healthy system, they are generally rare. When soil biology is diverse, these opportunistic organisms do not thrive. They are outcompeted by other organisms.

When you think of your garden, don’t think, “I need to blast this grub problem”, tempting though it may be. Trust me, when I find a plant that has been devastated by a pest, I wanna do battle too. Observe some of these factors and guidelines: first, you must always grow a little more than you need. When organic methods are used (and honesty even when chemical pesticides are used), you will always have a plant succumb to disease. That is just part of the circle of life. Second, observe whether or not the plant is weak and not getting what it needs–weak plants tend to succumb to disease and though aphids may be attacking at the moment, there is the possibility that your plant is susceptible because it is not getting it’s needs met (not enough light, incorrect watering, incorrect season, etc.). Third, if a pest is taking over, there may be a general imbalance. And most likely it is the damage we have done by feeding, spraying, with the intent to do good.

There is a world of biology inside a handful of compost.

Adding well made compost into your soil does not just feed plants, it inoculates your soil with live organisms. These organisms eat each other, poop, die, and create conditions that provide food for your plants. They have their own drama going on that sometimes has nothing to do with your plants. But when they take up that space, they leave little room for opportunistic organisms.

Don’t worry, I will get to the nematodes….

Some ways to make your soil a happy place for these beneficial organisms: Keep soil aerobic. Loose, not compacted soil, enriched with compost, organic material, food for all those critters, helps too. Mulch (I use a layer on the top of compost and finish with a layer of straw) is the icing on the cake.

If you raise a good compost pile, you will be adding beneficial nematodes (among a huge host of other beneficial organisms). But it helps to also inoculate the soil with an extra treatment of nematodes, so long as you try to follow all the other guidelines for healthy soil.

Predatory nematode eating another nematode.

Nematodes are microscopic, non-segmented roundworms (don’t gross out) that occur naturally in soil all over the world. Inside the nematode reside symbiotic bacteria that  kill prey when released from the nematode. The nematodes enter the larvae of insects found in the soil via the mouth, anus, respiratory openings, or directly through the body wall of the pest. The nematodes then eject their symbiotic bacteria inside the pest’s body. The bacteria multiply and cause blood poisoning of the pest, leading to death. The bacteria also convert host tissue into nutritive products, which can easily be taken up by nematodes. Inside the dead insect, the nematodes feed and multiply. As the food resources within the dead pest become scarce, the nematodes will exit the dead insect and immediately start searching for a new host.

There are different types of nematodes, divided into two broad groups: stationary and mobile. It’s really best to get a little bit of each sort of nematode, to control different types of pests.

When you add nematodes to the soil you most likely will not notice the effect. You may notice over time a decrease in particular insects that are predatory to your plants. You may just notice your plants doing better, and not know exactly why (because you could not see the underground problems that resided before the nematodes were introduced to the system).

I get my beneficial nematodes from Arbico. I will apply several types in spring and fall to a new garden plot. If the soil is maintained healthy, I won’t need to reapply. I also add some to the compost system after it has gone through the thermal stage (the part where the pile heats up). Generally you release them during the spring and fall, but follow instructions given by the source for your nematodes.

This grub succumbed to nematodes.

There will be more articles about particular types of beneficial organisms, and pests too. But I really want to impress the idea that we stop thinking of the garden as a battle zone. Rather, I would love to think of the garden as a living system that needs all its parts considered: the plants, the insects, the microorganisms, the organic material, the fungi…think about making the system healthy.

There is disturbance in nature. When a fire or flood ravages the land, for example, you have conditions similar to when humans take a bulldozer to a landscape. You wipe out the biology. We do the same when we spray pesticides, though we think we are helping the plants. You hurt most biological organisms good and bad when you spray. In nature, after disturbance, you have what we call succession, which is the natural evolution of the landscape from disturbed lifeless soil, into a diverse old-growth system (whether that old growth be cactus forest or redwood forest).

In nature, it takes a long time for succession to occur, weedy air distributed plants come into the area first(and opportunistic organisms) which eventually give way to small shrubs, and slightly more diversified soil biology. The small shrubs give way to trees, and the soil becomes even MORE diversified, more fungal dominated. This is healthy soil. We can learn a lot about how to grow plants considering how plants in nature perform. Because, obviously, in nature, nobody needs to go spraying pesticides or fertilizer. And plants have been around, evolving unthinkably longer than we have been cultivating the way we do. In fact, it was only during the advent of the industrial revolution that such practices came to be.


3 thoughts on “Beneficial Nematodes, Invisible Helpers Balance Soil Biology

  1. Nematodes are the most numerous multicellular animals on earth. A handful of soil will contain thousands of the microscopic worms, many of them parasites of insects, plants or animals. Free-living species are abundant, including nematodes that feed on bacteria, fungi, and other nematodes, yet the vast majority of species encountered are poorly understood biologically. There are nearly 20,000 described species classified in the phylum Nemata .

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